Join collection of strings into comma-separated string

Joiner.java

    public static String join(String separator, Iterator<String> iterator) {
        StringBuilder builder = new StringBuilder();

        while (iterator.hasNext()) {
            String token = iterator.next();
            if (token != null && !token.isEmpty()) {
                builder.append(token);
                break;
            }
        }

        while (iterator.hasNext()) {
            String token = iterator.next();
            if (token != null && !token.isEmpty()) {
                builder.append(separator);
                builder.append(token);
            }
        }

        return builder.toString();
    }